July is wet across the bulk of the country but is still warm. The dry zone including Mandalay & Bagan is still worth visiting in the summer as it has relatively little rain throughout the year. So perhaps creating a multi-centre holiday with other parts of South East Asia would be the best idea if you had to travel in July. The benefit of travelling in July is that the countryside will be starting to green up as new growth starts to appear. The beaches are now closed for the summer and roads to the more remote reaches could be difficult so if visiting best to stick to the main tourist destinations.